The invention discloses a tackifier for an oil-based drilling fluid and a preparation method of the tackifier. The tackifier comprises the following components in parts by mass: 2-5 parts of modifiedorganic soil, 2-4 parts of modified vegetable gum, 1-3 parts of thermoplastic elastic resin, 5-10 parts of acrylic acid, 3-5 parts of hydroxymethyl cellulose, 1-3 parts of a quaternary ammonium salt,0.5-1.5 parts of an emulsifier, 3-6 parts of base oil and 0.05-0.15 part of an initiator, wherein the modified organic soil is preferably activated and modified bentonite, the modified vegetable gum is preferably hydroxypropyl guar gum, and the initiator is a mixture of ammonium sulfate and sodium sulfite in a mass ratio of 1: (2-4). The tackifier for the oil-based drilling fluid can overcome thedefect that a water-based drilling fluid tackifier is not applicable to the oil-based drilling fluid, is beneficial for reducing the preparation cost of an oil-based drilling fluid system and improving the overall environmental protection performance of the oil-based drilling fluid, and plays an important role in improving the performance of the oil-based drilling fluid and application of the oil-based drilling fluid.